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Home , Transcritical cycle

Part A

1. CO2 – A historic perspective

2. Properties of CO2 CO as a 3. The transcritical CO2 cycle 2 4. Examples of CO2 systems

Prof. Dr.-Ing. Armin Hafner Professor Refrigeration Technology NTNU, EPT 7491 Trondheim Norway

GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017 2

Inventors and pioneers of mechanical refrigeration Vapour compression cycle: – Oliver Evans (1755-1819), USA ”The Abortion of the Young Steam Engineer’s Guide”, 1805 1. CO – A historic perspective – Jacob Perkins (1766-1849), American living in London 2 British Patent No 6662, 14. August 1834 Machine applying sulphur-ether, build by John Hague

Prof. Dr.-Ing. Armin Hafner Professor Refrigeration Technology NTNU, EPT 7491 Trondheim Norway

GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017 4

Inventors and pioneers of mechanical refrigeration Inventors and pioneers of mechanical refrigeration Air cycle: Absorption cycle: – John Gorrie (1802-1855), Florida, USA – Ferdinand Carré (1824-1900), France

”An for ventilation and cooling air in tropical climates by mechanical ” 1842-1844 Patent NH3/H2O absorption system in 1859

London World Exhibition 1861

GIAN @ Indian Institute of Technology Madras; October 2017 5 GIAN @ Indian Institute of Technology Madras; October 2017 6 Three important ‘drivers’ in the late 19th century 150 years ago: ICE = refrigeration

Factors pushing the development of mechanical refrigeration technology from 1850  Source: Disney

 “Artificial” ice production  Brewing of beer (all year long)  Transport of meat

Norwegian Ice Export from 1860 to 1915 GIAN @ Indian Institute of Technology Madras; October 2017 7 GIAN @ Indian Institute of Technology Madras; October 2017

Natural working fluids also common in the US: Three important ‘drivers’ in the late 19th century

Factors pushing the development of mechanical refrigeration technology from 1850 

 “Artificial” ice production  Brewing of beer (all year long)  Transport of meat

Advertisement in ICE and REFRIGERATION, 1922, vol. 63 GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017 10

Three important ‘drivers’ in the late 19th century th Why CO2 disappeared in the early/mid 20 century? Factors pushing the development of mechanical

refrigeration technology from 1850  • Leading within the industry (along with NH3) until the 90 1940s 80 Le Frigorifique, Buenos Aires – Rouen 1876-77 CO2 • Surpassed by synthetic CFCs and HCFCs (R-12, R- 70 R22  “Artificial” ice 22) in the 1950-60s due to 60 R12 production – Problems with leaks % 50 – Reduced cooling capacity at elevated rejection 40 temperatures  Brewing of beer (all 30 – Cold cooling water not available everywhere (especially USA) 20 NH3 year long) – Development and offensive marketing of CFC’s (”Freon”) 10 – Opinion that high working are a problem  Transport of meat 0 – Missing production- and material-technology 1940 1950 1960 1970 1980 1990 2000 – The safety standards and laws reduced the motivation to apply CO2 in the US more than in Europe. Percentage application of working fluids for ship refrigeration cold stores verified by Lloyd’s from Stera – 1. world war in Europe (1992)

GIAN @ Indian Institute of Technology Madras; October 2017 11 GIAN @ Indian Institute of Technology Madras; October 2017 12 Rediscovered as a working fluid in the 1980s by professor Gustav Lorentzen CO2 is back! (1915-1995)

First draft made for a patent application on how to (2000)

operate and control transcritical CO2- vapour compression systems November 1988

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Restricted use of synthetic working fluids

• CFC/HCFCs cause ozone depletion (Montreal protocol, 1987) • HFCs induce green house effects (Kyoto protocol 1997, EU F- regulation 2. Properties of CO 2006/2014) 2

• Strong position for natural working fluids

Prof. Dr.-Ing. Armin Hafner Professor Refrigeration Technology NTNU, EPT 7491 Trondheim Norway

GIAN @ Indian Institute of Technology Madras; October 2017 15 GIAN @ Indian Institute of Technology Madras; October 2017

Content CO2 in a HSE perspective

•COin a HSE perspective •CO2 is not acutely toxic at low concentrations. Bodily reactions (difficulties 2 breathing, increased pulse, headache, etc.) appear when the concentration • Fundamental fluid properties exceeds 2-3 %. Concentrations above 10 % can be lethal. • Significance of low critical temperature • Similar to the traditional high GWP*-HFCs, CO2 has the ASHRAE safety • Significance of high in the triple point classification A1 (non-flammable, non-toxic). • Consequences of high operational pressure • High operational pressure (up to 130 bar). • Heat transfer properties of CO2 • Dry ice formation can appear at pressures < 5.2 bar (triple point pressure), • Volumetric expansion coefficient for CO2 in state which can block valves and pipes. Important with sufficient routines regarding refilling and service of CO2 systems. • Dry ice at atmospheric pressure is very cold (~ -78 Ԩ) and can cause: – Brittle fractures in equipment – Frostbite injury * GWP =

GIAN @ Indian Institute of Technology Madras; October 2017 17 GIAN @ Indian Institute of Technology Madras; October 2017 18 CO2 in a HSE perspective Fundamental fluid properties

•CO2 is a natural and environmentally friendly working fluid: • Low critical temperature (TC = 31.1℃) GWP = 1 (0)*, ODP = 0 –28℃: Practical upper limit for condensation Component(s) Classification Concentration limit GWP – Heat rejection at supercritical pressures except kg/m3 at very low heat sink temperatures R‐744 A1 0.1 1 • High critical pressure (73.8 bar) R‐22 Chlorodifluoromethane A1 0.3 1810 • High pressures compared to other R‐23 Trifluoromethane A1 0.68 14800 working fluids R‐125 Pentafluoroethane A1 0.37 3500 – Typically 5 to 10 times higher than for HFC

R‐134a Tetrafluoroethane A1 0.21 1430 – Relatively low pressure ratio (Pgc/PE) R‐404A R‐125/R‐143A/R‐134a A1 0.52 3920 • Triple point pressure above atmospheric R‐407C R‐32/R‐125/R‐134a A1 0.31 1770 pressure (5.18 bar) R‐407F R‐32/R‐125/R‐134a A1 0.32 1820 – Equilibrium between 3 phases: Solid, liquid and vapour. R‐408A R‐125/R‐143a/R‐22 A1 0.41 3150 – Sublimation: Dry ice does not melt but rather evaporates. Sublimation temperature at atmospheric

pressures for solid CO2 is -78.5 ℃ *No formation of CO2 when used as a working fluid GIAN @ Indian Institute of Technology Madras; October 2017 19 GIAN @ Indian Institute of Technology Madras; October 2017 20

Fundamental fluid properties diagram for CO2 Danfoss Video • Superior heat transfer properties Supercritical pressure – Large volumetric heating capacity (VHC) Critical Subcritical pressure – Steep pressure curve (Δt/Δp): low point temperature loss per unit pressure loss • Large volumetric expansion coefficient in liquid state

GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017 22

Significance of low critical temperature (tC = 31.1℃) Significance of low critical temperature

COP for a freezing process at - 40℃ CO does not condensate above the critical • In comparison to other working fluids CO2 has a slightly 2 Transcritical cycle lower theoretical Coefficient of Performance (COP) during pressure - Three possible operational modes: Subcritical cycle subcritical operation. – Subcritical process: Max condensation temperature of 28 Ԩ, but • Large throttling losses when the condensation preferably much lower. Often necessary with a cascade system for temperature is close to the critical point. The same is true heat rejections at higher temperature. R-507 Pressure [bar]Pressure CO if the CO2 temperature after the gas cooler in a 2 NH3 – Transcritical process: Heat rejection above the critical point. No transcritical cycle is high. condensation - CO2 is cooled in the gas cooler at gliding • Consequence: The theoretical COP is lower for CO2 than COP Theoretical temperatures. (Normal) of the fluid in subcritical region [kJ/kg] (h) at constant temperature. for traditional working fluids.

• However, CO2 has proven more efficient than

Very efficient when heating a media over a large temperature ] traditional working fluids in real life applications. range, i.e. domestic hot water (from 10-20 °C to 70-90 ℃). ℃ p = constant Condensation temperature, ℃ (100bar) – Low pressure ratio (PC/PE)  Less compression – Low temperature losses (Δt/Δp): can be – Processes that alter between subcritical and transcritical: designed for high pressure loss  enhances heat transfer Operation based on heat sink temperature. Subcritical operations if [ Temperature – Small compression due to extremely high the heat sink allows it, as this would traditionally be most energy efficient when not utilizing access heat. [J/kg*K] (s) GIAN @ Indian Institute of Technology Madras; October 2017 23 GIAN @ Indian Institute of Technology Madras; October 2017 24 Significance of high pressure in the triple point Consequences of high operational pressure

• Possible dry ice formations during system •CO2 saturation pressure interventions (i.e. maintenance) as generally high compared to other working fluid. Ptriple-point > Patm. • The pressure increases • Generally formed if the pressure of liquid CO2 is decreased during: according to the – Filling/draining curve during heating of a CO2 – Blowout of pressure regulative valves/ safety valve liquid/vapour mixture. • Possible formation of solid ice blockage • Specific volume (m3/kg) is the • Evaporation temperature limited to the Solid CO relationship between the 2 container volume (m3) and the theoretic triple point temperature ( ~ -56 ℃) amount of media stored (kg). • Research within the area of CO dry ice 2 • Final pressure can be found in the interception between the specific volume sublimation (These “” can achieve -78 ℃) curve and maximum temperature.

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Consequences of charge Consequences of high operational pressure LP=Low pressure, MP=mid-pressure, HP= high pressure

Critical density • Dimensioning of equipment is done Direct Type of Direct expansion (DX) according to the specific pressures in CO2 expansion (DX) system system with R404A system with CO2 • Not economical to dimension all equipment Suction Pressure[bar] critical point in the system for maximum pressure pipe line, return 76/102mm 42/68mm Isochoric lines: • Much smaller dimensions for pipelines and Liquid 3 valves –mainly due to low viscosity and equal density [kg/dm ] line 35mm 22/48mm very low Δt/Δp Surface • 20-40 % lower weight of pipelines despite 100 % (reference) 60 % ratio Temperature [°C] higher wall thickness GIAN @ Indian Institute of Technology Madras; October 2017 27 GIAN @ Indian Institute of Technology Madras; October 2017 28

Consequences of high operational pressure Consequences of high operational pressure Pressure ratio at -40 ℃ evaporation

• Lower pressure ratio  NH3 lower required work input • High vapour density at high CO2 pressures – Smaller compression volume ratio Pressure Condensation temperature, ℃ required

–CO2: 15-20 % volume compared to traditional working fluids CO2 •  Smaller installations? • Higher •  Less investment cost? NH3 Relative compressionvolume efficiency

Relative required compression volume at -30/0 ℃ evaporation

and 20 ℃ condensation Isentropicefficiency Pressure ratio GIAN @ Indian Institute of Technology Madras; October 2017 29 GIAN @ Indian Institute of Technology Madras; October 2017 30 Consequences of high operational pressure Heat transfer properties of CO2 Measured heat transfer coefficient as a function of vapour fraction

• Smaller change in • High conductivity temperature due to NH pressure loss 3 • High specific

• and Δt/Δp condenser can be dimensioned for higher CO velocities 2 R-22

Temperature, ℃

GIAN @ Indian Institute of Technology Madras; October 2017 31 GIAN @ Indian Institute of Technology Madras; October 2017 32

Volumetric expansion coefficient for CO2 in liquid state References M. Bredesen, A. Hafner, J. Pettersen, P. Nekså, K. Aflekt: «Heat transfer and pressure drop for in-tube • Liquid normally has a low evaporation of CO2», IIR Proceedings 1997-5 «Heat Transfer in Natural », College Park . However, close (USA), November 6-7, 1997 Critical Hrnjak, P., Young Park, C., 2006: «CO2 Evaporation at Low Temperature». C-Dig Meeting, March 16-17, to the critical point (20-30 ℃) point 200 CO2 is partially compressible. • Due to the high thermal Partially compressible area

expansion coefficient, CO2 will expand with 25 % when heated from -10 to 20 ℃. • 3.5 - 5 times higher compared to other working fluids. • Increased danger of rupture

when overfilling fluid in CO2 system.

GIAN @ Indian Institute of Technology Madras; October 2017 33 GIAN @ Indian Institute of Technology Madras; October 2017 34 33 34

Content

• Background • Transcritical process in the Pressure-enthalpy (P-h) diagram 3. The transcritical CO2 cycle • Temperature change in the gas cooler • The influence of gas cooler pressure on COP • Optimum high pressure control

Prof. Dr.-Ing. Armin Hafner Professor Refrigeration Technology NTNU, EPT 7491 Trondheim Norway

GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017 36 Background Transcritical process in the Pressure-enthalpy (P-h) diagram • The transcritical CO cycle is 2 Suction gas exceptional for domestic hot water heat exchanger T= constant

heating (high temperature lift) Heat Gas cooler rejection • 1980s: Research was done within the area of commercializing heat for domestic hot water Throttling valve T= constant Compressor • 2001: The 6 kW EcoCute heat The Sanyo EcoCute System Evaporator [bar] Pressure was introduced to the Low pressure Japanese market receiver (LRP) Heat • 2017: More than 5 million units collection Enthalpy [kJ/kg] installed in Japan

GIAN @ Indian Institute of Technology Madras; October 2017 37 GIAN @ Indian Institute of Technology Madras; October 2017 38

Transcritical process in the Pressure-enthalpy Temperature change in the gas cooler (P-h) diagram

Suction gas heat exchanger T= constant ]

Heat ℃ Gas cooler rejection

Throttling valve

T= constant [ Temperature Compressor Evaporator [bar] Pressure

Low pressure receiver (LRP) Heat collection Enthalpy [kJ/kg] Enthalpy [kJ/kg]

GIAN @ Indian Institute of Technology Madras; October 2017 39 GIAN @ Indian Institute of Technology Madras; October 2017 40

Temperature change in the gas cooler Temperature difference in the gas cooler – pinch temperature – temperature approach

Example: Pinch point inside ] ℃ • Ideal heat transfer in HX: Completely parallel • The temperature approach, ΔTa, is the temperature temperature curves difference between the fluids at the gas cooler outlet ] •ΔTa expresses how adaptable the system is to [ Temperature • For non-linear temperature curves, the ℃ temperature difference in the HX is limited by transcritical operations Transferred heat [kW] the pinch point (minimum temperature • Large ΔTa difference) – Large throttling losses ]

Temperature [ Temperature – Low cooling capacity • Pinch point typically inside the gas cooler ℃ (low pressures) or at the outlet – Low COP Good • Important to consider when deciding the •ΔTa should not be lager than 2-4 K

Transferred heat [kW] solution! [ Temperature amount of fluid circulation (kg/s)

Transferred heat [kW]

GIAN @ Indian Institute of Technology Madras; October 2017 41 GIAN @ Indian Institute of Technology Madras; October 2017 42 Temperature in the gas cooler The influence of gas cooler pressure on COP – heating demand at different temperatures CO2 gas cooler outlet temperatures

Combined operation • Transient operations are especially Preheat water ]

convenient when delivering heat at ℃ Low temperature space heat Reheat water

different temperatures, ie. domestic hot COP water, space heating, etc. • Challenging to reach optimal efficiency if [ Temperature the different heating demands vary

• Perfect for modern flats / dwellings with Specific enthalpy [kJ/K] 50%+ share of hot water demand / total Gas cooler pressure, bar heating demand (dependent on climate zone)

20°C & 85 bar CO2 85°C & 85 bar GIAN @ Indian Institute of Technology Madras; October 2017 43 GIAN @ Indian Institute of Technology Madras; October 2017 44

The influence of gas cooler pressure on COP The influence of gas cooler pressure on COP • High(er) pressure and is sometimes better than low pressure and • High pressure regulation no subcooling: • Mechanical or electronic regulation of – 65 bar, subcooling to 10 ℃  COP = 5.8 valves – 60 bar, no subcooling  COP = 5.5 • The pressure can be controlled according

Saturation line to the CO2 temperature before throttling – For traditional cooling unit without heat recovery – Predetermined pressure/temperature curve – Necessary with electronic regulator and motor controlled throttling valve COP • Selecting the best control strategy Regulation characteristics for optimal gas cooler pressure – Function of the system (ie. purely cooling vs. cooling and heat recovery) – Gas cooler pressure control and fan speed regulation CO2 gas cooler outlet temperature [°C]

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References

G. Lorentzen: Revival of carbon dioxide as a refrigerant. Int. J. Refrig. Vol. 17, No. 5 1993

Jørn Stene: Residential CO2 System for Combined Space Heating and Hot Water Heating, Doctoral Thesis at NTNU 2004:53 4. Examples of CO2 systems K. B. Madsen: Transcritical CO2 System in a Small Supermarked. Danfoss-seminar om CO2 som kuldemedium, Oslo, 21.01.2009

Petter Nekså, Håvard Rekstad, G. Reza Zakeri and Per Arne Schiefloe: CO2-heat pump water heater, characteristics, system design and experimental results, Int. J. Refrig., Vol. 21, No. 3, pp 172-179, 1998

Prof. Dr.-Ing. Armin Hafner Professor Refrigeration Technology NTNU, EPT 7491 Trondheim Norway

GIAN @ Indian Institute of Technology Madras; October 2017 47 GIAN @ Indian Institute of Technology Madras; October 2017 Content DOWNLOAD for FREE! •CO2 as an evaporating secondary fluid

•CO2 in a conventional cooling process (cascade system)

• Transcritical CO2 process with low-pressure receiver

• Transcritical CO2 process with mid-pressure receiver

• Transcritical CO2 process with low and mid-pressure receivers

• Transcritical CO2 booster system

GIAN @ Indian Institute of Technology Madras; October 2017 49 GIAN @ Indian Institute of Technology Madras; October 2017

CO2 as an evaporating secondary fluid CO2 as an evaporating secondary fluid

• Application: Condenser Free cooling with CO2 Condenser

– Subcritical CO2 system with NH3 in the • Free cooling loop included primary loop • System must be dimensioned for – Supermarkets, industrial freezers, ice rinks Compressor Compressor standstill pressure ( No evaporation Primary loop Primary loop • Advantages: assistance system!) – Flooded evaporator

Throttling valve Evaporator/condenser – Oil free CO2 loop Throttling valve Evaporator/condenser – High efficiency Liquid receiver Liquid receiver – Smaller pipe dimensions and pump work Evaporation assistance Secondary loop compared to glycol circuits system Secondary loop • Disadvantages: CO pump Cooling Cooling 2 – Complicated CO pump batteries Avoids pressure build-up 2 batteries – Expensive e.g. during stand still

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CO2 in a conventional cooling process CO2 in a conventional cooling process Condenser - cascade systems - cascade systems Condenser • Application: – Two separate refrigeration units • Application: Second stage – Large facilities with need for refrigeration at Second stage system – First stage subcritical CO2 system Compressor Compressor system several temperature levels Throttling valve – Second stage system with a working fluid suitable for Throttling valve heat rejection (NH3, propane (R290), etc.) • Advantages: CO2 Cascade heat exchanger – Utilized in supermarkets pre-transcritical cycle Cascade heat exchanger (CHX) – Flooded chiller evaporator compressor Liquid receiver • Advantages: Liquid receiver – Compact CO2 – Energy efficient process Evaporation First stage compressor First stage assistance system • Disadvantages: system system – Small operational cost Throttling – Expensive valve Throttling valve Evaporator, chiller – The indirect system provides NH3 leakage precaution – The CO2 system fully relies on the second CO2 Evaporator, freezer stage system for condensation pump • Disadvantages: Evaporator – Problematic if the second stage system is inactive – Challenging to regulate the CHX at small capacities without variable speed drive GIAN @ Indian Institute of Technology Madras; October 2017 53 GIAN @ Indian Institute of Technology Madras; October 2017 54 Transcritical CO process: Important considerations 2 Transcritical CO2 process with mid-pressure receiver

• Application: Gas cooler • Gas cooler pressure – Single throttling step Transcritical cycle • Placement of receivers – Smaller installations Subcritical cycle – Norild, Sonyo, Denso • Single vs. several throttling steps Compressor • Advantages: • Mid pressure control – LRP enables flooded evaporation Suction gas heat exchanger – Dual throttling steps – High suction pressure than with TEV – Lower vapour quality before throttling due to the LPR with/cooling suction gas heat exchanger coils • Disadvantages:

– Single evaporator Evaporator Pressure regulative valve – Oil boil-off – Slow start-up due to liquid accumulation in LPR

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Gas cooler Gas cooler Transcritical CO2 process with mid-pressure receiver

Gas cooler • Application: Bypass valve Compressor – Two throttling steps Compressor – Simple regulated systems Pressure regulative valve Pressure regulative valve Pressure differential valve Suction gas heat exchanger • Advantages: Mid pressure receiver (MPR) Constant pressure valve

– Uncomplicated transcritical process Compressor – No connection between gas cooler pressure Mid pressure receiver (MPR) and feed to evaporator Throttling valve Mid pressure receiver (MPR)

• Disadvantages: Throttling valve Evaporator Evaporator – Superheat at evaporator outlet Throttling Regulation of gas cooler pressure by constant Active regulation of receiver pressure with flash – Oil boil-off Evaporator valve pressure difference – Passive mid pressure gas bypass through constant pressure valve – Slow start-up due to liquid accumulation in regulation MPR

GIAN @ Indian Institute of Technology Madras; October 2017 57 GIAN @ Indian Institute of Technology Madras; October 2017 58

Transcritical CO process with low and mid-pressure 2 Transcritical CO2 booster system receivers Gas cooler Gas cooler • Application:

Pressure – Two stage compression and throttling regulative valve HP- • Benefits from both LPR and MPR – Leading solution in larger systems Compressor

– Flooded evaporator • Advantages: Pressure regulative valve – Enables higher suction pressure Compressor – Robust and well developed Constant Intermediate – No connection between gas cooler pressure pressure valve Suction gas – Standard components and regulation gas cooler control and feed to evaporator Mid pressure heat receiver exchanger – Strong competitor to NH3 systems in the industry (MPR) – Well known and applicable all over the world Mid pressure receiver (MPR) LP- low pressure Compressor receiver • Disadvantages: (LPR) – Gas cooler outlet temperature in the range of 25-35℃

Throttling valve

Evaporator Throttling valve Evaporator

GIAN @ Indian Institute of Technology Madras; October 2017 59 GIAN @ Indian Institute of Technology Madras; October 2017 60 Gas cooler Gas cooler Cascade CO CO2 booster system 2 HP- booster system References HP- compressor compressor • Smaller investment • Avoid problems due A. Hafner, T. S. Nordtvedt, E. Gukelberger, K. Banasiak, K. Widell: Design of a R717/R744 Cascade System for the cost Suction gas HX Pressure to oil-return Pelagic Fish Industry. 11th IIR Gustav Lorentzen Conference on Natural refrigerants, Hangzhou, China, 2014 Suction gas HX Pressure • Higher efficiency regulative regulative • Possible to utilize oil valve Dr. A. B. Pearson (editor): CO2 as a Refrigerant. IIR GUIDES. International Institute of Refrigeration, 2014. ISBN: valve of different MPR Constant pressure valve 978-2-36215-005-0 MPR Constant pressure valve viscosities for chiller and freezer Hillphoenix Refrigeration Systems: Second Nature CO2 Capable of Making a Difference. evaporators http://www.hillphoenix.com/refrigeration-systems/second-nature/ Throttling valve Ole Christensen: Typical ammonia/CO2 Cascade System, Freezing and Cooling Application. Technical Paper 1, 2006 Throttling Evaporator, valves chiller IIAR Ammonia refrigeration Conference & Exhibition, Reno, Nevada, USA Evaporator, chiller S. Forbes Pearson, Ph.D.: Using CO2 To Reduce Refrigerant Charge. ASHRAE Journal vol. 54, no. 3, October 2012 Cascade HX LP-compressor shecco guide: Examples of NH3 /CO2 Secondary Systems for Cols store Operators. LP- compressor https://issuu.com/shecco/docs/guide_nh3-final Suction gas HX Stene, J., 1988: Guidelines for Design and Operation of Compression Heat Pump, Air Conditioning and Refrigerating Suction gas HX systems with Natural Working Fluids. IEA Heat Pump Programe, report no. HPP-AN22-4. ISBN 90-73-741-31-9.

Y. Solemdal, T. M. Eikevik, I. Tolstorebrov, O.J. Veiby: CO2 as a Refrigerant for Cooling of Data-Center: A Case Throttling Throttling th valve Study. 11 IIR Gustav Lorentzen Conference on Natural Refrigerants, Hanszhou, China, 2014 valve

Evaporator, Evaporator, freezer freezer GIAN @ Indian Institute of Technology Madras; October 2017 61 GIAN @ Indian Institute of Technology Madras; October 2017 62

A wise man said Thank you for your attention 22 years ago

Contact: We have heard a great deal lately of the harmful effects to the environment when halocarbon refrigerants are lost to the [email protected] atmosphere. This should not really have Prof. Gustav Lorentzen (1915-1995) come as a surprise since similar problems have happened over and over again. Numerous cases are on record where new chemicals, believed to be a benefit to man, have turned out to be environmentally unacceptable, sometimes even in quite small quantities (DDT, PCB, Pb etc.).

In the present situation, when the CFCs and in a little longer perspective the HCFCs are being banned by international agreement, it does not seem very logical to try to replace them by another family of related halocarbons, the HFCs, equally foreign to nature.

Int. Journal of Refrigeration 9. Vol. 18, No. 3, pp 190 197, 1995 GIAN @ Indian Institute of Technology Madras; October 2017 GIAN @ Indian Institute of Technology Madras; October 2017